Robotic radiosurgery systems, such as CyberKnife™, use a high-precision robotic manipulator, with an image-guided system delivering beams of radiation to the target from multiple predefined beam directions. A robotic arm is used to position a radiation source in order to achieve flexibility in aiming radiation beams. Robot-controlled radiation devices, of which the Cyberknife™ radiosurgery system is one example, contain a linear accelerator (LINAC) mounted on a robotic arm allowing beams of radiation to be directed from any angle. This design is typically referred to as a non-isocentric design. These radiation delivery systems do not usually rotate around a fixed center or axis; therefore, a set of pre-programmed positions is often configured into the system's software to produce repeatable and accurate targeting. A pre-programmed position is defined as a node, and a set of pre-programmed positions (nodes) is defined as a “path”.
In order to achieve the accuracy of SRS treatment, each node in a path must be calibrated to a high degree of precision. Most commonly, each node is calibrated so that the radiation beam axis precisely passes through a certain reference point, the alignment center, from a predefined angle. Once initially calibrated (during installation), subsequent verifications are needed to confirm that at each node the radiation beam continues to precisely pass through the alignment center from the predefined angle. The present invention provides an accurate and simple apparatus and method to accomplish the subsequent verification. Prior to the present invention, there is no apparatus or method to accomplish this verification accurately and quickly.